As bar codes and other symbologies used to encode packaging labels grow more dense, the optical path of an electronic scanner often must be focused in order to successfully read the code or symbol. High speed package handling operations which use bar codes or other symbologies to identify packages typically require rapid automatic focusing mechanisms which must operate at high speed for prolonged periods of time. The high package quantities processed by such systems require the automatic focusing mechanism employed to have a very long life. For example, in certain applications, the focusing mechanism may be required to perform as many as one million focusing cycles per year without breakdown.
In conventional automatic focusing systems, image focusing is achieved by holding the focal plane of an image receptor in a stationary position and moving a focusing lens. In such systems, the lens is typically moved by mounting the lens in a screw mount and turning the mount with a small servo motor. Such conventional systems are not suitable for cameras which must be focused and refocused quickly and repetitively over prolonged periods of time. For example, a conventional automatic focusing system could not be successfully employed to perform overhead scanning of a continuous stream of packaging labels of varying height positioned on a rapidly moving belt. Due to the high mass of their moving parts, conventional automatic focusing systems are unable to achieve the very fast focusing slew times required by such applications. In addition, due to the friction and wear between moving parts in conventional automatic focusing systems, such systems are unable to perform continuously in high volume operations for prolonged periods of time.
It is therefore an object of the present invention to provide an automatic focusing system capable of reliably performing in a high speed automated environment for prolonged periods of time.
It is a further object of the present invention to provide an automatic focusing system which does not require the movement of high mass parts to achieve focusing.
It is a still further object of the present invention to provide an automatic focusing system which operates with a minimum of friction and wear between its moving parts.
Further objects and advantages of the invention will become apparent from the description of the invention which follows.